1. Field of the Invention
The invention relates to techniques for monitoring and surveying a subsurface reservoir penetrated by a well. More particularly, the invention concerns a method, and a device for its implementation, in which a tubular adapted for permanent disposal is deployed in a borehole. One or more antennas are disposed on the tubular to measure the reservoir properties in a desired direction by selectively steering the sensing direction of electromagnetic energy transmitted and/or received by the antenna(s) and by disposing an antenna on the tubular such that its axis is tilted with respect to the axis of the tubular. The invention has a particularly advantageous application in the collection of information on the displacement of hydrocarbons and water in a subsurface reservoir.
2. Description of Related Art
Petroleum is usually produced from oil reservoirs sufficiently far below a gas cap and above an aquifer. As the oil zone is being produced and depleted, the gas cap starts coning downward and the aquifer coning upwards towards the oil bearing zone. Such migration can adversely affect the extraction of petroleum by creating pockets that are missed by the producer and by saturating the oil deposits with water. As soon as either gas or water hits the well, its oil production usually ceases instantly.
Reservoir monitoring includes the process of acquiring reservoir data for purposes of reservoir management. Permanent monitoring techniques are used for long-term reservoir management. In permanent monitoring, sensors are permanently implanted in communication with the reservoir to be managed. For example, in one approach, sensors are permanently situated inside the casing to measure phenomena inside the well such as fluid flow rates or pressure. U.S. Pat. No. 5,467,823 (assigned to the present assignee) describes a technique for monitoring the pressure of the fluid in the reservoir. EP 0964134 A2 describes a power and signal transmission technique for permanent downhole installations using casing with external reservoir sensors.
Reservoirs are also monitored for changes in saturation and early signatures of coning so that corrective action can be taken. Measuring the electrical resistivity (or its inverse, conductivity) of the formations surrounding a borehole has been used to determine production zones in oil and gas fields and to map sand and shale layers. Electrical resistivity depends directly on porosity, pore-fluid resistivity, and saturation. Porous formations having high resistivity generally indicate the presence of hydrocarbons, while low-resistivity formations are generally water saturated.
U.S. Pat. No. 5,642,051 (assigned to the present assignee) describes a technique incorporating electrodes mounted on the casing exterior to pass a current through the reservoir to measure its electrical resistivity. U.S. Pat. No. 5,992,519 (assigned to the present assignee) describes a technique for active or automated control of a reservoir using a combination of valves and sensors disposed in the wellbore. U.S. Pat. No. 6,023,445 describes a technique for monitoring contact levels of fluids in an oil reservoir. The technique of the ""445 patent uses a wireline tool disposed in a monitoring well to take acoustic measurements. U.S. Pat. No. 5,829,520 describes a technique for monitoring a reservoir using an extendable sensor attached to a tubular. U.S. Pat. No. 5,461,594 describes a method for monitoring the displacement of fluids in a reservoir using receivers disposed in a wellbore to detect seismic signals. A primary disadvantage of all these techniques is the inability to steer or focus the measurement of the reservoir property to a specifically desired region.
Thus, there remains a need for an improved method and apparatus for monitoring reservoir properties. It is desirable to implement a technique that provides for long-term selective focusing or steering of reservoir measurements without affecting production.
The invention provides an apparatus for monitoring a characteristic of a reservoir. The apparatus includes a tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within a borehole traversing the reservoir. At least one antenna is disposed on the exterior of the tubular, each antenna having an axis and being adapted for transmission and/or reception of electromagnetic energy. The antenna is disposed on the tubular such that its axis is tilted with respect to the axis of the tubular, and means to activate the antenna to transmit and/or receive electromagnetic energy are provided.
The invention provides another apparatus for monitoring a characteristic of a reservoir. The apparatus includes a tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within a borehole traversing the reservoir. An antenna is disposed on the exterior of the tubular, the antenna being adapted to transmit and/or receive electromagnetic energy. Means to activate the at least one antenna to selectively steer the sensing direction of the transmitted and/or received electromagnetic energy are also provided.
The invention provides another apparatus for monitoring a characteristic of a reservoir. The apparatus includes a tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within a borehole traversing the reservoir and has at least one slot formed along its elongated body. At least one antenna is disposed on the exterior of the tubular, each antenna having an axis and being adapted for transmission and/or reception of electromagnetic energy. At least one antenna is disposed on the tubular in alignment with a slot, and means to activate at least one antenna to transmit and/or receive electromagnetic energy are provided.
The invention provides another apparatus for monitoring a characteristic of a reservoir. The apparatus includes a tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within a borehole traversing the reservoir. At least one saddle coil is disposed on the exterior of the tubular, each saddle coil is adapted for transmission and/or reception of electromagnetic energy, and means to activate the saddle coil to transmit and/or receive electromagnetic energy are provided.
The invention also provides a method for monitoring a reservoir characteristic, the reservoir being traversed by a borehole. The method includes disposing a tubular within the borehole, the tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within the borehole and has at least one antenna disposed on its exterior, each antenna having an axis and being adapted for transmission and/or reception of electromagnetic energy. The method also includes disposing the antenna on the tubular such that its axis is tilted with respect to the axis of the tubular, and activating the antenna to transmit and/or receive electromagnetic energy.
The invention provides another method for monitoring a characteristic of a reservoir, the reservoir being traversed by a borehole. The method includes disposing a tubular within the borehole. The tubular having an elongated body with a longitudinal axis and adapted for permanent disposal within the borehole. The method also includes disposing an antenna on the exterior of the tubular, the antenna being adapted to transmit and/or receive electromagnetic energy; and selectively steering the sensing direction of the transmitted and/or received electromagnetic energy.
The invention provides another method for monitoring a reservoir characteristic, the reservoir being traversed by a borehole. The method includes disposing a tubular within the borehole, the tubular having an elongated body with a longitudinal axis. The tubular is adapted for permanent disposal within the borehole and has at least one slot formed along its elongated body with at least one antenna disposed on the exterior of the tubular in alignment with a slot, each antenna is adapted for transmission and/or reception of electromagnetic energy. The method also includes activating the antenna to transmit and/or receive electromagnetic energy.
The invention provides another method for monitoring a characteristic of a reservoir, the reservoir being traversed by a borehole. The method includes disposing a tubular within the borehole. The tubular has an elongated body with a longitudinal axis and is adapted for permanent disposal within the borehole. The tubular has at least one saddle coil disposed on its exterior; each saddle coil is adapted for transmission and/or reception of electromagnetic energy. The method also includes activating the saddle coil to transmit and/or receive electromagnetic energy.